Wastewater treatment entails removing and treating many different types of pollutants or contaminants found in wastewater. Various processes are known and available in the art, but the basic approaches revolve around biological and/or chemical treatment processes. Generally, solid components in the wastewater are removed via mechanical separation, for instance with the aid of screens and grit chambers and by allowing the solid impurities to settle in a preliminary settling device. This is followed by a chemical treatment process and preferably also by a biological treatment process.
Chemical treatment generally involves the use of precipitation chemicals, such as iron salts or aluminum salts, which react with, flocculate, and/or precipitate impurities in the wastewater such as phosphates.
Flocculation, or coagulation, plays a central role in this process, where dissolved and colloid impurities are destabilized and large floc aggregate are formed, which can be removed from the water in subsequent clarification or filtration process. The speed of flocculation and the quality of the floc aggregates formed is central to the effectiveness of the treatment process, not only because it affects the removal of the soluble or colloid impurities from the water, it also affects the characteristics (e.g. sludge quantity, volume, compactness and water content) of the sludge formed, which must also be treated.
The chemicals or flocculation agents commonly used for municipal wastewater treatment include alum and lime as well as a range of synthetic polymers. It is important to add the minimum amount of chemicals possible and to obtain good contact with all of the wastewater to reduce costs, maximize efficiency and minimize the amount of sludge.
In the biological treatment process, which can take place, for instance, by an activated sludge process or by means of a trickling filter, the wastewater is purified by the actions of microorganisms.
Removal of phosphorus from wastewater is essential in any wastewater treatment process, because high bio-available phosphorus in the water, if discharged into natural water streams, will cause many adverse effects on the environment. Generally, bio-available phosphorus (e.g. orthophosphate) is the limiting nutrient in freshwater aquatic systems. Increased concentration of available phosphorus allows plants to assimilate more nitrogen before the phosphorus is depleted. Thus, if sufficient phosphorus is available, elevated concentrations of nitrates will render the water eutrophic and lead to algal blooms. “Algal blooms” refers to generally to nutrient-induced production of aquatic plants in both freshwater and estuaries. Detrimental consequences of algal blooms include odors and discoloration caused by algal mats and decaying algal clumps, which will interfere with recreational and navigational water uses; oxygen depletion which interferes with aquatic fauna and in extreme cases can lead to death of desirable fish species, and disruption of the composition of native flora due to altered nutrient profiles.
Phosphorus reduction is now an active target by the EPA. In some states, every wastewater operation is required to monitor daily levels of phosphorus in their effluent. Additionally, some operations are already permitted for phosphorus reduction at levels from 0.3 mg/litter (ltr) to 1.0 mg/ltr, with 1.0 mg/ltr being the most typical.
The current accepted approach involves the addition of certain chemicals, with ferric chloride and alum being the most dominant choices in the industry. It is generally accepted that the addition of sufficient volumes of either of these chemicals will guarantee acceptable phosphorus reduction. Typically, commercial suppliers suggest that 200 mg/ltr of ferric chloride or alum as being sufficient for adequate phosphorus reduction, to meet permit requirements. For example, in the state of Minnesota, addition of ferric chloride or alum are a “process requirement” for obtaining permits for wastewater operations.
Chitosan has been used in water treatment in the pool and spa industry, as well as in treatment of storm water, but not in the wastewater industry. Like currently available chemicals such as ferric chloride and alum, the high cost of using chitosan has restricted its use. In addition to cost concerns, the high volumes of these material required to achieve acceptable results have resulted in increased sludge volume in wastewater treatment plants where they have been used.
Additionally, when alum is applied regularly, the resulting aluminum-containing sludge is known to inhibit microbial and other biological and biochemical processes that are required for activated sludge to degrade contaminants in the wastewater. Paradoxically, the use of ferric chloride and alum also causes a condition referred to as ‘chemical dependency’ by operational personnel in municipal wastewater operations. In other words, when chemicals such as ferric chloride or alum are used, the microbial population in a wastewater operation tend to become dependent upon the continued use of the chemicals in order to function efficiently.
Chemical additions are also a concern because of their corrosive qualities and the risk in handling them. These corrosive effects lead to decreased life expectancy of equipment and other physical structures of the wastewater treatment plant, increasing the cost of operation.
Therefore, there are needs for improved methods and compositions that solve these problems.